At present, plug-in cards that have been widely used in storage devices, such as Input/Output (I/O) cards, are usually equipped with heat sinks for cooling the plug-in cards. In some conditions, a larger heat sink may be needed to provide better heat dissipation performance so as to ensure normal operation of the plug-in card. However, a larger heat sink may have a greater thickness, while the chassis panel usually has openings with limited opening height. Therefore, the heat sink with greater thickness may create obstacles during the hot plug operation of the plug-in card.